Enhancement after keratorefractive lenticule extraction: incidence, timing, refractive patterns, and management in a 3,396-eye single-center registry

Background The literature on enhancement after keratorefractive lenticule extraction (KLEx) remains limited, particularly when retreatment frequency is anchored to a large real-world denominator. The purpose of this study was to evaluate the incidence, timing, refractive patterns, and management of secondary enhancement after KLEx in a large single-center clinical registry and to examine whether a revised treatment nomogram introduced on July 1, 2024 was associated with lower subsequent enhancement frequency. Methods A retrospective registry study was performed at Eye Clinic Svjetlost, Zagreb, Croatia. The denominator registry comprised 3,396 KLEx eyes treated on the SCHWIND ATOS platform. Enhancement eyes were identified from dedicated cap-to-flap and transepithelial photorefractive keratectomy (TransPRK) workbooks. Main outcomes were enhancement rate, time to enhancement, pre-enhancement refractive characteristics, technique distribution, observed postoperative uncorrected distance visual acuity (UDVA), and paired ocular and corneal wavefront outcomes. Because postoperative corrected distance visual acuity (CDVA) was not systematically captured, an exploratory surrogate CDVA analysis was performed using pre-enhancement CDVA and observed postoperative UDVA; the safety index derived from this analysis represents an upper-bound estimate. Exact era denominators were 1,198 eyes before July 1, 2024 and 2,198 eyes on or after July 1, 2024. Results A total of 61 eyes of 48 patients underwent enhancement, corresponding to an overall enhancement rate of 1.80% (61/3,396; 95% confidence interval [CI], 1.38% to 2.30%). Median time to enhancement was 4.1 months (interquartile range [IQR], 2.7 to 5.5 months; range, 1.1 to 51.0 months), and 47 of 61 eyes (77.0%) were enhanced within 6 months. Mean pre-enhancement spherical equivalent (SEQ) was − 0.80 ± 0.72 D (range, − 2.25 to 1.00 D). Forty eyes underwent cap-to-flap conversion and 21 underwent TransPRK. Cap-to-flap conversion was technically successful in 39 of 40 eyes (97.5%). In harmonized analyses, mean observed UDVA improved from 0.18 ± 0.18 to − 0.03 ± 0.10 logMAR at 1 month (n = 41, P < .001) and from 0.15 ± 0.12 to − 0.05 ± 0.08 logMAR at 3 months (n = 20, P < .001). Ocular wavefront metrics remained stable. Corneal trefoil at 6 mm increased modestly from 0.18 ± 0.09 to 0.22 ± 0.13 µm (n = 58, P = .035) without correlation to latest observed UDVA. Era analysis showed 46 enhancements among 1,198 eyes treated before July 1, 2024 (3.84%) versus 15 among 2,198 eyes treated thereafter (0.68%), corresponding to an 82.2% relative reduction (χ² = 43.82, P < .001; risk ratio for post- versus pre-nomogram enhancement frequency, 0.18, 95% CI 0.10 to 0.32). Conclusions Secondary enhancement after KLEx was uncommon in this 3,396-eye registry and usually occurred early after primary surgery. A revised age-adjusted nomogram introduced on July 1, 2024 was associated with a markedly lower enhancement frequency in the subsequent era. Cap-to-flap conversion and TransPRK were both viable enhancement strategies in routine practice, but the principal contribution of this study is denominator-anchored reporting of enhancement incidence, timing, and workflow rather than proof of optical superiority between enhancement techniques.